1. Field of the Invention
The present invention generally relates to deposition of a metal layer onto a substrate. More particularly, the present invention relates to a substrate holder system for use in an electrochemical plating (ECP) system to deposit a metal film on a substrate.
2. Background of the Related Art
Electroplating is used for the fabrication of lines on circuit boards as well as to fill features, such as vias, trenches, and electric contact elements, for example, in semiconductor devices. A typical feature-fill process including electroplating comprises depositing a barrier layer over the feature surfaces by a process such as physical vapor deposition (PVD) or chemical vapor deposition (CVD), then depositing a conductive metal seed layer such as copper on the barrier layer by a process such as PVD or CVD, and then electroplating a conductive metal film over the seed layer to fill the feature and form a blanket layer on the field to form the desired conductive structure. The deposited metal film is then planarized by a process such as chemical mechanical polishing (CMP) to define a conductive interconnect feature. An electric contact ring is commonly positioned in contact with the seed layer on the substrate during electroplating to supply electricity to the seed layer.
A number of obstacles impair reliable electroplating onto substrates having micron-sized, high aspect ratio features. One of these obstacles relates to a substrates, held by a substrate holder assembly, being immersed in a level attitude into electrolyte solution. The substrate holder assembly typically includes an electric contact ring, or a support ring, that extends around the periphery of the substrate. The electric contact ring or a support ring typically physically supports the substrate during electroplating. Portions of the substrate holder assembly, such as electric contact rings or support rings, together with the substrate define a downwardly-facing concave surface. As the substrate holder assembly is immersed with the substrate, the concave surface defined by the substrate and substrate holder assembly can trap air that form air pockets within the electrolyte solution.
The air bubbles or the air bridges that are trapped in the electrolyte solution by the concave surface defined by the substrate holder assembly and substrate can contact the surface of the substrate during plating. The electrolyte solution does not physically contact those portions of the seed layer on the substrate that the air bubbles or air bridges contact. Metal film, therefore, cannot be deposited on those portions of the seed layer that the air bubbles or air pockets cover. As such, the existence of air bubbles or air bridges adjacent the seed layer during metal film deposition can affect the uniformity of the depth of the deposited metal film across the seed layer. Limiting the amount of air bubbles or air bridges that contact the seed layer during processing and providing a uniform electric current density across the seed layer on the substrate during plating.
The existence of air bubbles within the features during deposition of the metal film can also limit the filling of the features on the substrate, and thereby lead to the creation of voids, or spaces, within features formed within the deposited metal film. The existence of voids in the features leads to unreliable, unpredictable, and unuseable electronic devices in the electronic circuit containing the feature.
Therefore, there remains a need for an electrochemical plating (ECP) system that limits the formation of air bubbles between the substrate and/or the substrate holder assembly during the immersion of the substrate into electrolyte solution.
The present invention generally provides an ECP system. More specifically, a method is performed by the electrochemical plating system in which a seed layer formed on a substrate is immersed into an electrolyte solution. In one aspect, a substrate is immersed in the electrochemical plating system by tilting the substrate as it enters the electrolyte solution to limit the trapping or formation of air bubbles in the electrolyte solution between the substrate and the substrate holder assembly. In another aspect, an apparatus is provided for electroplating that comprises a cell and a substrate holder system. The substrate holder system can displace the substrate holder assembly in the x and z directions and also tilt the substrate. In another aspect, a method is provided of driving a meniscus formed by electrolyte solution across a surface of a substrate. The method comprises enhancing the interaction between the electrolyte solution meniscus and the surface as the substrate is immersed into the electrolyte solution.